The present invention provides a sterilizing fog, characterized by droplet size range, vapor density range, sterilant concentration range and sterilant concentration within the droplets. Specifically, the inventive fog is achieved by an apparatus combining pressure, temperature and acoustics to form a super-charged ozoneated water and an apparatus that creates small micro droplets which form a highly concentrated sterilizing fog. Specific sterilants used are ozone, chlorine and chlorous acid generating compositions such as sodium hypochlorite.
Food processing and food safety has increasingly relied upon techniques to remove or eliminate harmful microbial organisms from the surfaces of food products. Harmful bacterial products have been found on meat food products, such as salmonella on poultry and E. coli H057 on various red meats. Various techniques have been developed to test for the presence of such harmful organisms but such tests, inherently, can only sample random surfaces and rely on probabilities to determine of all of the surface area of food products has either been free of such harmful organisms or effectively decontaminated.
There are many broad-spectrum sterilizing agents that are strong oxidants, such as chlorine, hypochlorite (bleach), hydrogen peroxide, and ozone or O3. Although chlorine is the most common sterilizing agent in the world, ozone is commonly used to sterilize hot tubs and other public swimming pools. In addition, poultry and other meat-processing that historically has relied solely on chlorine, now frequently baths chickens in water containing ozone. However, in order for the ozone, or chlorine or any other sterilant in water to be effective, the sterilizing agent is present in a sufficient concentration within water and in contact with the organisms (and the chicken) for a sufficient period of time (inversely related to concentration) to allow the oxidizing agent to contact and kill microorganisms. It is difficult to achieve such high concentrations in an aqueous liquid. In a gaseous form most sterilizing agents are rather hazardous and difficult to control exposure time. Ozone decays in a gaseous form far too quickly to be useful for food processing. Thus, water is the preferred media for transporting ozone, chlorine, and hypochlorite to a contaminated site for oxidative anti-microbial activity.
Unfortunately, the realities of food processing are such that many food products cannot be immersed in a liquid bath (e.g., most fresh meat products and even some dry products like grains) although some moisture is allowed contact. In those instances where water immersion is not permitted, spray systems have been developed to spray a water-laden with oxidizing agent. However, spray systems do not provide a uniform coverage of the product and can utilize large amounts of water. Accordingly, spray systems employing larger droplets of water containing ozone, chlorine or hypochlorite have not been effective because of a droplet size that is too large to effect food surface penetration of irregularities. Moreover, the lower concentrations of sterilizing agents achievable in such spray systems, coupled with short exposure times, do not provide for effective oxidizing potentials and anti-microbial activity to be sufficiently effective as a decontaminating process. This is especially true of chlorine and hypochlorite that require long exposure times.
A further issue is that liquid sterilization systems or spray systems with large droplets are unable to penetrate micro-cavities on irregular surfaces of food products, such as meats (e.g., poultry or bovine). Water surface tension prevents the large drops and liquid baths from penetrating these regions and the bacteria present in micro-cavities remains undisturbed (FIG. 1 left panel).
Therefore, there is a need in the art to be able to better utilize the anti-microbial power of ozone, chlorine, hypochlorite, and other sterilizing agents, particularly within the context of food processing of meat products having irregular surfaces to hide bacteria from exposure to oxidizing agents. The present invention was made to solve this need.
The present invention provides an sterilizing agent-laden fog useful for disinfecting irregular surfaces wherein the fog comprises water and a sterilizing agent selected from the group consisting of ozone, hypochlorite, chlorine and combinations thereof, wherein the fog is characterized by droplets having an average diameter of from about 0.0005 mm to about 0.05 mm, a weight of fog concentration in a treatment space is of from about 0.08 g/m3 to about 0.8 g/m3. Preferably, the concentration of ozone in water of from about 0.5 ppm to about 30 ppm, the concentration of chlorine in water of from about 10 ppm to about 100 ppm, and the concentration of sodium chlorite of 0.001% to about 0.65% by weight based upon the total weight of said composition of sodium chlorite, whereby the chlorite ion concentration in the form of chlorous acid is not more than about 15% by weight of the total amount of chlorite ion concentration. Preferably, sterilizing agent is an aqueous solution consisting essentially of from about 1% to about 6% by weight of citric acid, and from about 0.001% to about 0.65% by weight based upon the total weight of said composition of sodium chlorite, such that the chlorite ion concentration in the form of chlorous acid is not more than about 15% by weight of the total amount of chlorite ion concentration.
The present invention further provides a sterilizing fog generator device for generating a sterilant fog having droplets of an average diameter from about 0.0005 mm to about 0.05 mm, comprising:
(a) an ozone gas injector for injecting gas into water and having a venturi nozzle; and
(b) a vapor cell communicating with the ozone gas injector nozzle, wherein the vapor cell has a bottom and side walls and comprises an ultrasonic focused transducer located on the bottom of the vapor cell and wired to an electronic amplifier and an orifice direct toward a target for the ozone fog. Preferably, the sterilant fog is an ozone fog wherein ozone concentrations of from about 0.5% to about 20% by weight. Preferably, the ultrasonic transducer is operated at multiple frequencies of from about 0.75 MHz to about 2.0 MHz and at multiple pulse shapes, whereby the frequency and pulsed irregular wave forms control droplet size of the fog produced. Preferably, the orifice has a diameter of from about 0.1 cm to about 8 cm whereby the orifice size determines the density of the ozone fog generated. Preferably, the present invention further comprises a plurality of the vapor cells, connected in series or in parallel, and communicating to the target for the ozone fog through a single orifice.
The present invention further provides a food disinfection immersion apparatus comprising
(a) a means for forming an ozone gas;
(b) a means for injecting the ozone gas into a water stream in an injection chamber, wherein the injection chamber further comprises a temperature controller, a pressure controller and an ultrasonic transducer to achieve the highest saturation level of gas in liquid; and
(c) an immersion tank for disinfecting the food comprising an entry port for feeding the highly concentrated ozone water, a means for suspending the food product, and one or a plurality of ultrasonic scrubbers that agitate the food product surface microcavities to allow for deeper penetration of the highly concentrated ozone water. Preferably, the food disinfection immersion apparatus further comprises a means for injecting sodium hypochlorite and chlorine solutions into a water stream.
The present invention further provides a method for disinfecting irregular surfaces, comprising contacting a product having an irregular surface for disinfecting with a sterilizing fog, wherein the ozone fog comprises water and a sterilizing agent and wherein the fog is characterized by droplets having an average diameter of from about 0.0005 mm to about 0.05 mm, a weight of fog concentration in a treatment space of from about 0.08 g/m3 to about 0.8 g/m3, and an ozone concentration in water of from about 0.5 ppm to about 30 ppm. Preferably, the product having an irregular surface is a food product. Most preferably, the food product is red meat or poultry.